Send postgresql log to syslog

Enable syslog to listen to udp port 514 (the port number can be changed to suit your need)

# vi /etc/rsyslog.conf

$ModLoad imudp

$UDPServerRun 514

Restart rsyslog

# systemctl restart rsyslog

Check if rsyslog is now listening to 514 udp port

# ss -tulpn | grep 514

udp    UNCONN     0      0                      *:514                   *:*      users:(("rsyslogd",15281,3))

udp    UNCONN     0      0                     :::514                  :::*      users:(("rsyslogd",15281,4))

Set postgres to log to syslog

# vi /var/lib/pgsql/9.5/data/postgresql.conf

log_destination = 'syslog'

Restart postgres

# systemctl restart postgresql-9.5

Check if your postgres log is now being logged by syslog

# tail -f /var/log/messages 

...

Dec 11 08:39:21 mypostgres postgres[21518]: [3-1] < 2018-12-11 08:39:21.932 UTC >LOG:  autovacuum launcher started

Install nvidia driver for Tesla card on ubuntu 16.04

Check what driver your card is currently using, in this case, the card is using the opensource nvidia drivers called nouveau
$ lspci -v | grep -A8 NVIDIA
3d:00.0 3D controller: NVIDIA Corporation Device 1bb3 (rev a1)
        Subsystem: NVIDIA Corporation Device 11d8
        Flags: bus master, fast devsel, latency 0, IRQ 40
        Memory at b7000000 (32-bit, non-prefetchable) [size=16M]
        Memory at 4bfe0000000 (64-bit, prefetchable) [size=256M]
        Memory at 4bff0000000 (64-bit, prefetchable) [size=32M]
        Capabilities:
        Kernel driver in use: nouveau
        Kernel modules: nvidiafb, nouveau

Download the driver for your card from nvidia download website

Choose the correct card model, and operating system, and click SEARCH

Click DOWNLOAD

Click AGREE & DOWNLOAD to download

If you want to download using wget, right click on the AGREE & DOWNLOAD button, and choose "Copy Link Address". Run wget against the link

$ wget http://us.download.nvidia.com/tesla/410.79/nvidia-diag-driver-local-repo-ubuntu1604-410.79_1.0-1_amd64.deb

Install the driver

$ sudo apt install ./nvidia-diag-driver-local-repo-ubuntu1604-410.79_1.0-1_amd64.deb

Make sure you have now nvidiafb in kernel modules 

$ lspci -v | grep -A15 NVIDIA

3d:00.0 3D controller: NVIDIA Corporation Device 1bb3 (rev a1)

        Subsystem: NVIDIA Corporation Device 11d8

        Flags: bus master, fast devsel, latency 0, IRQ 40

        Memory at b7000000 (32-bit, non-prefetchable) [size=16M]

        Memory at 4bfe0000000 (64-bit, prefetchable) [size=256M]

        Memory at 4bff0000000 (64-bit, prefetchable) [size=32M]

        Capabilities: [60] Power Management version 3

        Capabilities: [68] MSI: Enable+ Count=1/1 Maskable- 64bit+

        Capabilities: [78] Express Endpoint, MSI 00

        Capabilities: [100] Virtual Channel

        Capabilities: [250] Latency Tolerance Reporting

        Capabilities: [128] Power Budgeting

        Capabilities: [420] Advanced Error Reporting

        Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024

        Capabilities: [900] #19

        Kernel driver in use: nouveau

        Kernel modules: nvidiafb, nouveau

Update

$ sudo apt update

Install cuda-drivers

$ sudo apt install cuda-drivers

Reboot your machine

$ sudo reboot

Check whether your card is using nvidia driver, and not nouveau

$ lspci -v | grep -A8 NVIDIA

3d:00.0 3D controller: NVIDIA Corporation Device 1bb3 (rev a1)

        Subsystem: NVIDIA Corporation Device 11d8

        Flags: bus master, fast devsel, latency 0, IRQ 88

        Memory at b7000000 (32-bit, non-prefetchable) [size=16M]

        Memory at 4bfe0000000 (64-bit, prefetchable) [size=256M]

        Memory at 4bff0000000 (64-bit, prefetchable) [size=32M]

        Capabilities:

        Kernel driver in use: nvidia

        Kernel modules: nvidiafb, nouveau, nvidia_410_drm, nvidia_410

Using tsocks with apt to bypass proxy

Recently, I encountered an error while trying to update ubuntu server 16.04. The error is as below:

E: Failed to fetch http://my.archive.ubuntu.com/ubuntu/dists/xenial/InRelease  Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)

It seems there is a proxy somewhere in the network, that I do not know. Asking around, even the owner of the server does not even know any proxy server inside their network. So, what I did was, create a socks proxy on my own, to a server outside of the network, and tunnel the apt connection using an application called tsocks.

First, you need to install tsocks. This is a bit tricky since we cannot use the apt command to download and install it from the internet. So I downloaded the deb file, using wget.

$ wget -c http://archive.ubuntu.com/ubuntu/pool/universe/t/tsocks/tsocks_1.8beta5-9.3_amd64.deb

Once downloaded, install using apt on the local file.

$ sudo apt install ./tsocks*.deb

Once installed, create a socks proxy to a server outside of the network, on localhost port 8888 (this is just my favorite number for socks proxy, you can use any number above 1000). You need to be able to ssh to the outside server for this to be possible.

$ ssh foo@server.outside -D 8888

Change the tsocks config file, to suite your new socks proxy

$ sudo cat /etc/tsocks.conf

# You just need to change these 3 lines

server = 127.0.0.1

server_type = 5

server_port = 8888

$ sudo -i 

# tsocks apt update

# tsocks apt upgrade

P/S: You can also set an environment variable called http_proxy, if you do not want to install tsocks, but this setting will be only active on your current bash session. This can be accomplished by:

# export http_proxy='socks5://localhost:8888'

# apt update && apt upgrade

Create a persistent reverse tunnel for a server behind firewall

To do this, you need to have a middleman server (middleman) to act as intermediaries between your workstation and the server behind firewall (target). The best is to have your middleman server running ssh server on the usual port that firewall allows, for example 80 and 443.

Step 1: In the target server, create a passwordless ssh access to your middleman server. Please refer here on how to accomplish that

Step 2: Create a simple bash script in target server that will check for the reverse tunnel connection, and restart the tunnel if the tunnel is broken. Lets say in this case, my middleman ssh server is running on port 443, you want to create a reverse tunnel on port 2222 on middleman server, and you want to use a user called foo in the middleman server. Don't forget to make the script executable by the owner.

$ cat /home/foo/bin/tunnelcheck.sh

#!/bin/bash

SERVER=middleman

SPORT=443

PORT=2222

USER=foo

ssh $USER@$SERVER -p $SPORT -t nc -vz localhost $PORT > /dev/null 2>&1

if [ $? -ne 0 ];

  then ssh -R $PORT:localhost:22 -l $USER -fN $SERVER -p $SPORT

fi

$ chmod u+x /home/foo/bin/tunnelcheck.sh


Step 3: Set a crontab to run the above script every 10 minutes (or whatever interval you think is appropriate)
$ crontab -e
*/10 * * * * /home/foo/bin/tunnelcheck.sh


Step 4: Test the persistency by killing the ssh tunnel, and wait for crontab to run the tunnelcheck.sh script, and restart the tunnel

Step 5: You are now able to access the target server, simply by ssh'ng into port 2222 on middleman server
$ ssh foo@middleman -p 2222

How to test that your usb live cd is working

To do this, you need qemu-kvm. Install it:
$ sudo apt install qemu-kvm


Check the address of your usb, by using dmesg
$ dmesg | grep sd


Once you have the address, you can start it using below command (make sure you allocate at least 1024M memory, else it will return kernel panic)
$ sudo qemu-system-x86_64 -m 1024 -hda /dev/sdb


To use a cdrom, you can use below command
$ sudo qemu-system-x86_64 -m 1024 -cdrom /dev/cdrom


You can also test an iso file, using below command
$ sudo qemu-system-x86_64 -m 1024 -cdrom centos.iso